Cytokinins are an important type of plant hormone. They have various effects including induction of cell division, formation of new buds, overcoming dormancy of axillary buds, prevention of aging and promotion of enlargement of fruit. Cytokinins have a structure in which a dimethylallyl group (isopentenyl group) bonds to a nitrogen atom at position 6 of adenine or adenosine, or has a structure in which the isopentenyl group is hydroxylated as their basic skeleton. Some bacteria that are pathogenic to plants are known to have cytokinin synthesis enzymes and among these, the cytokinin synthases of IPT and TZS of Agrobacterium are known to have activity that transfers the dimethylallyl group of dimethylallyl pyrophosphoric acid (DMAPP) to the nitrogen atom at position 6 of adenosine monophosphate (AMP). This reaction is considered to be the most important step in cytokinin synthesis. However, cytokinin synthesis enzymes possessed by plants and the proteins that encode them have yet to be identified.